In February 1760 delegates of the Haudenosaunee (Iroquois) réductions (reserves) of Oswegatchie, Kanesatake and Kahnawake sought assurances for the "22 Nations in the French interest" that the Six Nations would not take up arms against them in the final battles of the Seven Years' War. The commander-in-chief of the British forces, General Jeffrey Amherst, issued a proclamation on 26 April designed to win over France's allies which said that "His Majesty has not sent me to deprive any of you of your Lands or Property," and promising that in return for their support they would be maintained in their "just rights," including their hunting territories.

When the British invasion force reached Fort Lévis [Johnstown, Ont] and the réduction of La Présentation in mid-August, William Johnson, superintendent of Indian Affairs, met with delegates of the "Seven Confederate Nations of Canada" and solemnly promised to secure to them the possession of their lands and the free exercise of the Catholic religion. France's former allies promised to remain neutral during the remainder of the war in return for a promise not to be treated thereafter as enemies.

The terms of the agreement were confirmed at a special meeting on 15-16 September 1760 at Kahnawake and reconfirmed on 21 August 1769. William Johnson in a letter to the British prime minister said that they "ratified a treaty with us." The Supreme Court of Canada upheld the status of the Treaty of Oswegatchie in 1994.